Blackbody radiating device with a protective hood



F/Li] 1968 A. G. DE BELL 3,419,709

' BLACKBODY RADIATING DEVICE WITH A PROTECTIVE HOOD Filed May 25. 1966INVENTOUR. 1 t 4272/02 6. D5ZL ATTO NE) United States Patent Office3,419,709 Patented Dec. 31, 1968 3,419,709 BLACKBODY RADIATING DEVICEWITH A PROTECTIVE HOOD Arthur G. De Bell, Woodland Hills, -Calif.,assignor to North American Rockwell Corporation, a corporation ofDelaware Filed May 25, 1966, Ser. No. 552,851 5 Claims. (Cl. 219553)ABSTRACT OF THE DISCLOSURE A blackbody radiating device containing aheatable oxidizable body in a housing having an open end exposing saidoxidizable body to ambient air. An opening in the wall of the :housingto provide a flow of inert gas over the oxidizable body and a protectivehood aflixed to the open end of the housing so designed as to cool saidinert gas when exiting from said open end 20 as to prevent egress ofdeleterious air into said housing.

This invention relates to a means for improving blackbody radiationdevices. More particularly, the invention relates to a means forimproving the life of the radiating element used in blackbody radiationdevices.

In Patent 3,205,343 assigned to the same assignee, there is disclosed ablockbody source. The source contains a radiating element which isgenerally made of graphite. The element is connected to an electricalsource which resistively heats it to temperatures at which the radiationoccurs. Erosion and oxidation of the graphite or other radiation elementcan be reduced by flushing with a slight flow of inert gas, such asargon. However, in operation it was found that a portion of the ambientatmosphere, which was usually air, would still enter the element throughthe end-viewing aperture. This, in turn, caused oxidation and erosion ofthe graphite element more rapidly than desired.

Thus, an object of this invention is to further enhance the life of agraphite or other oxidiza-ble element used in blockbody radiationdevices.

Another object of the invention is to provide a means for reducing thequantity of inert gas needed to protect the radiation element.

The object of this invention is accomplished by afiixing to the viewingend of the blackbody device a protective hood which is comprised of awater-cooled jacket extension. As will be shown in the descriptionaccompanying the figures, the extension prevents the air from enteringthe cavity of the blackbody device and causing any deleterious effect.The invention will be described in further detail with relation to thefollowing drawings in which:

FIG. 1 is a partially sectioned view of a blackbody radiation devicewithout the improvement of the invention.

FIG. 2 is a section of a blackbody radiation device incorporating theprotective hood of the invention.

Referring now to FIG. 1, there is shown a blackbody radiation device 11which essentially corresponds to the type of device shown in FIG. 3 ofthe referred to US. Patent 3,205,343. The details of the device otherthan the graphite radiating element are not of import to the hereininvention and, thus, no details of the portion of the device extendingfrom the front half of the graphite element toward the rear are shown.As described in the mentioned patent, the device contains an outercylindrical shell or housing 13. Disposed concentrically within thehousing is a radiation element 15 which is of a material such asgraphite. A radiation surface 17 is medially disposed within thecylindrical radiating element and serves to radiate toward the open end19. An aperture 21 is provided at the open end 19 to view the radiatingsurface 17. To prevent oxidation of the radiating element, aninert noblegas is admitted into the device and flows through a passage 23surrounding the element. The inert noble gas then enters the elementthrough apertures 25 and flows within the cavity 27 between theradiating surface 17 and the end 19 of the device. The inert gas whichcan be argon is shown by the solid line arrows in the drawing.

The argon enters, as described, the blackbody cavity through theapertures 25. It is heated in the blackbody, which is at 2000 K., toabove 450 K. At this temperature, the argon becomes less dense than air.The heavier air, as depicted by the dotted arrows, enters at the bottomof the aperture 21 and forces the argon out through the upper portion ofthe aperture. As the air scours the bottom of the hot graphite cavity,it causes erosion by oxidation principally along the surface 29, whichis the bottom portion of the cylindrical graphite element when thedevice is used in its normal horizontal position as shown. This erosioneventually causes failure of the blackbody radiation element 15.

Turning now to FIG. 2 there is shown the improvement of the inventionwherein a protective hood 31 is threadably affixed at 33 to the frontportion 19 of the blackbody radiation device. The cylindrical hood hasan outer wall 33 and an inner corrugated wall 35. Between these walls isformed a cavity 37. An inlet 39 is provided to the cavity with an outlet41 also in the wall 33 of the device. A coolant such as water enters theinlet 39, circulates within the cavity 37 and exits at the outlet 41.The corrugated surface 35 serves to increase the effective heat transferarea between the coolant and the gases within the hood. Additionally, asshown, the corrugated inner wall 35 is shown in a generallyfrusto-conical configuration, tapering outwardly from the exit of theblackbody radiation device. This serves to allow the full field of viewof the heated cavity to be utilized. Due to the utilization of theprotective hood, the hot argon leaving the aperture 21 of the blackbodydevice is cooled by contact with the water-cooled protective hood 31.The argon then drops below 450 K. and becomes heavier than the air. Thisforms a protective curtain which is effective in preventing the air fromentering the aperture. As can be seen from the dotted arrowsrepresenting the air, the air progresses only slightly inwardly withinthe protective hood, but does not come close to reaching the confines ofthe blackbody cavity 27. This serves to prevent the erosion, previouslydescribed, of the graphite element and greatly prolongs the lifethereof. Additionally, less inert gas is required to effect the desiredresult of protecting the graphite from air.

For example, as a possible alternative to the arrangement shown in FIG.2, the coolant water circulating in the hood extension 31 can pass fromthe hood into the main body 13 of the device to cool the walls thereof.With this particular arrangement, an aperture can be provided betweenthe coolant passages 33 of the main body of the radiation device and thehood, wherein the water can exit from the hood into the coolant passages33.

Though the device has been shown utilizing a liquid cooled outerprotective jacket or hood, it is contemplated that in certain instancesthe air cooled one can be utilized. In those instances where the problemis not so severe, such as in a smaller aperture at lower temperature, amere air cooled protective hood will suffice. Thus, in accord with theconcept of the invention, the protective hood should extend a length andbe cooled to the degree necessary to prevent air from entering theblackbody cavity. As indicated, this occurs by keeping the temperatureof the inert gas at a point where it is heavier than the air so as toform a protective curtain.

The invention as described in the attached figures has been withrelation to the particular blackbody radiation device shown and claimedin the previously issued patent as referred to above. However, it ispointed out that the blackbody radiating element in such a device, ascontemplated, does not of necessity have to have the peculiarconfiguration shown and claimed in that patent. Rather, the concept ofthe herein invention relating to the protective hood is applicable inany oxidizable radiating or heated element. Thus, in virtually any shaperadiating or heated element which is open to the environment, theattendant problem of corrosion and erosion from ambient air would beovercome by the utilization of the protective hood of this invention.

The use of the hood as shown has an application which is obviously farbroader than the particular blackbody radiating element. In blackbodyradiating elements, .a window has been used over the opening throughwhich readings are taken. The window, however, presents opticalproblems. With the removal of the window, as shown in the particulardevice of the previous patent, the attendant problem of erosion fromambient air occurs. This same problem is prevalent in various furnacesand other heated bodies which are exposed to the air and require acontinuous flow of inert gas to protect the heated bodies fromoxidation. In all instances, if sufficient quantities of inert gas wereavailable, then there would not be a need for a protective device asshown. The quantities of inert gas that would be required are in factoften unattainable or impractical. Thus, the herein invention presentsbotha simple, easy, and in some cases, the only means for preventing therapid and gross deterioration of a radiating or heated element due tocontact with air.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

I claim:

1. In a device containing a heatable oxidizable body in a housing havingan open end exposing said oxidizable body to ambient air, and means inthe wall of said housing defining an opening to flow an inert gas oversaid oxidizable =body egressing from said opening is provided, theimprovement which comprises:

a protective hood affixed to said open end of said housing and extendingaway from said oxidizable body, said hood of suflicient length andhaving suificient heat absorbing characteristics whereby said inert gasis sufliciently cooled when exiting from said open end so as to preventegress of deleterious air into said housing.

2. In a blackbody radiating device comprising:

a housing provided with opening at one end thereof for an emittingradiation,

a blackbody radiation element disposed within said housing, said elementopen at one end thereof, said open end aligned with said open end ofsaid housing for emitting radiation from the interior of said element,

a radiating surface disposed within said blackbody element, whereby oneside of said surface is exposed for viewing through said open end ofsaid housing,

means for admitting an inert gas within said blackbody element betweensaid partition and said open end,

the improvement which comprises:

a protective hood atfixed to said open end of said housing and extendingaway from said blackbody element, said hood being of sufficient lengthand having sufficient heat absorbing characteristics whereby said inertgas is suificiently cooled when exiting from said open end so as toprevent ingress of deleterious air into said housing.

3. The improvement of claim 2 wherein said protective hood is adouble-walled body.

4. The improvement of claim 3 wherein said hood is provided with meansfor circulating a coolant therethrough.

5. The improvement of claim 2 wherein said hood is frusto-conical.

References Cited UNITED STATES PATENTS 2,952,762 9/1960 Williams et al2l9-553 X 3,138,697 6/1964 Banca et al 219-353 3,205,343 9/1965 De Bellet al 219--553 3,263,016 7/1966 Branstetter et al 13-26 FOREIGN PATENTS1,078,795 5/1954 France.

OTHER REFERENCES The Review of Scientific Instruments, R. H. McFee,Blackbody Source Unit With Electronic Temperature Control, January 1952,vol. 23, No. 1, pp. 52-53 (copy in 219553).

BERNARD A. GILHEANY, Primary Examiner.

V. Y. MAYEWSKY, Assistant Examiner.

US. Cl. X.R.

